This type of fluid control system has a flow rate sensor and a flow rate adjusting valve arranged on a flow channel in which a fluid flows, and is so configured to conduct feedback control on the flow rate adjusting valve so as to make a measured flow rate of the fluid measured by the flow rate sensor equal to a target flow rate by means of an integrally or separately provided control circuit.
At a time when the fluid begins flowing, namely when control of the flow rate is initiated from the fully open state toward a target flow rate, if the feedback control is conducted from the measured flow rate, it may take time for the measured flow rate to settle at the target flow rate. This is because the flow rate adjusting valve does not begin moving unless the value of the driving signal exceeds a certain threshold. Then, if the feedback control for calculating the driving signal value (the applied voltage) of the flow rate adjusting valve, in accordance with the deviation between the target flow rate and the measured flow rate, is performed from the target flow rate, the applied voltage calculated in the first several control loops does not exceed the threshold so that the time for the first several control loops until the flow rate adjusting valve actually begins moving is wasted.
It is a matter of course that it is possible to improve responsiveness by setting the applied voltage output based on the deviation so as to immediately exceed the threshold by increasing a control coefficient, however, with this arrangement, it is very probable that oscillation is generated so that the control becomes unstable.
Then, in the patent document 1, at a time when the flow rate control is initiated from the fully closed state, the applied voltage that is first output is compulsorily set to be a value exceeding the threshold, and the value is assumed to be the initial value (the initial applied voltage) and the feedback control is initiated with this initial value.